BACTERIA that resist antibiotics are a growing problem worldwide, but one we thought we could limit or even reverse by better control of the drugs. This may be a forlorn hope: some bacteria that have never seen an antibiotic can evolve resistance, and even thrive on it. Bacteria usually become resistant if they are exposed to drug levels too low to kill them off, but high enough to favour the survival of resistant mutants. Such resistance is growing and could make TB and other diseases untreatable again.
